Iterative pilot tone cancellation for improved channel estimation and decoding

ABSTRACT

Channel estimation is performed in a wireless network through cell/antenna pair ranking and iterative soft cancellation of pilot signals. Cell classification and ordering may be ranked and grouped for purposes of improving performance by dedicating hardware resources to higher priority received signals. A metric may be computed to rank the pairs. One such metric is reference signal (RS) power. Pairs may also be grouped into groups of pairs. Groups may be ordered by time-frequency resource and designated as serving-cell groups or non-serving cell groups. Higher priority pairs may be assigned a higher number of iterations. Higher priority groups may be processed first. Pairs which fall below a certain power threshold may be assigned no iterations. Iterations are distributed among hardware blocks to improve processing efficiency. Iteration numbers and hardware assignments may be modified to reach a desired complexity constraint.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patentapplication No. 61/385,780 filed Sep. 23, 2010, in the names of MALLIK,et al., the disclosure of which is expressly incorporated herein byreference in its entirety.

BACKGROUND

1. Field

Aspects of the present disclosure relate generally to wirelesscommunication systems and, more particularly to, iterative pilot tonecancellation for improved channel estimation and decoding.

2. Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. A wireless communication network may include a number of basestations that can support communication for a number of user equipments(UEs). A UE may communicate with a base station via the downlink anduplink. The downlink (or forward link) refers to the communication linkfrom the base station to the UE, and the uplink (or reverse link) refersto the communication link from the UE to the base station.

A base station may transmit data and control information on the downlinkto a UE and/or may receive data and control information on the uplinkfrom the UE. On the downlink, a transmission from the base station mayencounter interference due to transmissions from neighbor base stationsor from other wireless radio frequency (RF) transmitters. On the uplink,a transmission from the UE may encounter interference from uplinktransmissions of other UEs communicating with the neighbor base stationsor from other wireless RF transmitters. This interference may degradeperformance on both the downlink and uplink.

As the demand for mobile broadband access continues to increase, thepossibilities of interference and congested networks grows with more UEsaccessing the long-range wireless communication networks and moreshort-range wireless systems being deployed in communities. Research anddevelopment continue to advance the UMTS technologies not only to meetthe growing demand for mobile broadband access, but to advance andenhance the user experience with mobile communications.

SUMMARY

Various aspects relate to the estimation of a serving channel by a UE.In various aspects, channel estimation is performed in a wirelessnetwork through cell/antenna pair ranking and iterative cancellationtechniques. Cell/antenna pair classification, ordering, ranking, andgrouping may provide improved techniques for assigning higher priorityresources or greater quantities of resources to higher priority pairs orgroups. Pairs or groups which fall below a certain power threshold maybe assigned few or no resources. Furthermore, processing iterations maybe distributed among available resources to improve processingefficiency or reach a desired complexity constraint.

Offered is a method of wireless communication. The method includesdetermining cell-antenna pairs associated with received transmissions ina received signal. The method also includes grouping the cell-antennapairs into groups. Each group includes cell-antenna pairs with collidingpilot tones. The method also includes ranking the groups according to adetermined metric. The method further includes assigning a number ofiterations to each ranked group. The method still further includesperforming channel estimation using iterative cancellation. In theiterative cancellation, received transmissions from cell-antenna pairsin a higher ranked group are iterated first, and received transmissionsfrom cell-antenna pairs are iterated over their assigned number oftimes.

Offered is an apparatus for wireless communication. The apparatusincludes means for determining cell-antenna pairs associated withreceived transmissions in a received signal. The apparatus also includesmeans for grouping the cell-antenna pairs into groups. Each groupincludes cell-antenna pairs with colliding pilot tones. The apparatusalso includes means for ranking the groups according to a determinedmetric. The apparatus further includes means for assigning a number ofiterations to each ranked group. The apparatus still further includesmeans for performing channel estimation using iterative cancellation. Inthe iterative cancellation, received transmissions from cell-antennapairs in a higher ranked group are iterated first, and receivedtransmissions from cell-antenna pairs are iterated over their assignednumber of times.

Offered is a computer program product for wireless communication in awireless network. The computer program product includes a non-transitorycomputer-readable medium having non-transitory program code recordedthereon. The program code includes program code to determinecell-antenna pairs associated with received transmissions in a receivedsignal. The program code also includes program code to group thecell-antenna pairs into groups. Each group includes cell-antenna pairswith colliding pilot tones. The program code also includes program codeto rank the groups according to a determined metric. The program codefurther includes program code to assign a number of iterations to eachranked group. The program code still further includes program code toperform channel estimation using iterative cancellation. In theiterative cancellation, received transmissions from cell-antenna pairsin a higher ranked group are iterated first, and received transmissionsfrom cell-antenna pairs are iterated over their assigned number oftimes.

Offered is an apparatus for wireless communication. The apparatusincludes a memory and a processor(s) coupled to the memory. Theprocessor(s) is configured to determine cell-antenna pairs associatedwith received transmissions in a received signal. The processor(s) isalso configured to group the cell-antenna pairs into groups. Each groupincluding cell-antenna pairs with colliding pilot tones. Theprocessor(s) is also configured to rank the groups according to adetermined metric. The processor(s) is further configured to assign anumber of iterations to each ranked group. The processor(s) is stillfurther configured to perform channel estimation using iterativecancellation. In the iterative cancellation, received transmissions fromcell-antenna pairs in a higher ranked group are iterated first, andreceived transmissions from cell-antenna pairs are iterated over theirassigned number of times.

This has outlined, rather broadly, the features and technical advantagesof the present disclosure in order that the detailed description thatfollows may be better understood. Additional features and advantages ofthe disclosure will be described below. It should be appreciated bythose skilled in the art that this disclosure may be readily utilized asa basis for modifying or designing other structures for carrying out thesame purposes of the present disclosure. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the teachings of the disclosure as set forth in the appendedclaims. The novel features, which are believed to be characteristic ofthe disclosure, both as to its organization and method of operation,together with further objects and advantages, will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present disclosure willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout.

FIG. 1 is a block diagram conceptually illustrating an example of atelecommunications system.

FIG. 2 is a diagram conceptually illustrating an example of a downlinkframe structure in a telecommunications system.

FIG. 3 is a block diagram conceptually illustrating an example framestructure in uplink communications.

FIG. 4 is a block diagram conceptually illustrating a design of a basestation/eNodeB and a UE configured according to an aspect of the presentdisclosure.

FIG. 5 is a block diagram illustrating a method for communicating in awireless network according to one aspect of the disclosure.

FIG. 6 is a block diagram illustrating cell-antenna pairs according toone aspect of the disclosure.

FIG. 7 is a block diagram illustrating a method for communicating in awireless network according to one aspect of the disclosure.

FIG. 8 is a block diagram illustrating a method for communicating in awireless network according to one aspect of the disclosure.

FIG. 9 is a block diagram illustrating components for communicating in awireless network according to one aspect of the disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. However, it will beapparent to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts.

The techniques described herein may be used for various wirelesscommunication networks such as Code Division Multiple Access (CDMA),Time Division Multiple Access (TDMA), Frequency Division Multiple Access(FDMA), Orthogonal Frequency Division Multiple Access (OFDMA),Single-Carrier Frequency Division Multiple Access (SC-FDMA) and othernetworks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology, suchas Universal Terrestrial Radio Access (UTRA), TelecommunicationsIndustry Association's (TIA's) CDMA2000®, and the like. The UTRAtechnology includes Wideband CDMA (WCDMA) and other variants of CDMA.The CDMA2000® technology includes the IS-2000, IS-95 and IS-856standards from the Electronics Industry Alliance (ETA) and TIA. A TDMAnetwork may implement a radio technology, such as Global System forMobile Communications (GSM). An OFDMA network may implement a radiotechnology, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB),IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, andthe like. The UTRA and E-UTRA technologies are part of Universal MobileTelecommunication System (UMTS). 3GPP Long Term Evolution (LTE) andLTE-Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA.UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents froman organization called the “3rd Generation Partnership Project” (3GPP).CDMA2000® and UMB are described in documents from an organization calledthe “3rd Generation Partnership Project 2” (3GPP2). The techniquesdescribed herein may be used for the wireless networks and radio accesstechnologies mentioned above, as well as other wireless networks andradio access technologies. For clarity, certain aspects of thetechniques are described below for LTE or LTE-A (together referred to inthe alternative as “LTE/-A”) and use such LTE/-A terminology in much ofthe description below.

FIG. 1 shows a wireless communication network 100, which may be an LTE-Anetwork, in which iterative pilot tone cancellation may be implemented.The wireless network 100 includes a number of evolved node Bs (eNodeBs)110 and other network entities. An eNodeB may be a station thatcommunicates with the UEs and may also be referred to as a base station,a node B, an access point, and the like. Each eNodeB 110 may providecommunication coverage for a particular geographic area. In 3GPP, theterm “cell” can refer to this particular geographic coverage area of aneNodeB and/or an eNodeB subsystem serving the coverage area, dependingon the context in which the term is used.

An eNodeB may provide communication coverage for a macro cell, a picocell, a femto cell, and/or other types of cell. A macro cell generallycovers a relatively large geographic area (e.g., several kilometers inradius) and may allow unrestricted access by UEs with servicesubscriptions with the network provider. A pico cell would generallycover a relatively smaller geographic area and may allow unrestrictedaccess by UEs with service subscriptions with the network provider. Afemto cell would also generally cover a relatively small geographic area(e.g., a home) and, in addition to unrestricted access, may also providerestricted access by UEs having an association with the femto cell(e.g., UEs in a closed subscriber group (CSG), UEs for users in thehome, and the like). An eNodeB for a macro cell may be referred to as amacro eNodeB. An eNodeB for a pico cell may be referred to as a picoeNodeB. And, an eNodeB for a femto cell may be referred to as a femtoeNodeB or a home eNodeB. In the example shown in FIG. 1, the eNodeBs 110a, 110 b and 110 c are macro eNodeBs for the macro cells 102 a, 102 band 102 c, respectively. The eNodeB 110 x is a pico eNodeB for a picocell 102 x. And, the eNodeBs 110 y and 110 z are femto eNodeBs for thefemto cells 102 y and 102 z, respectively. An eNodeB may support one ormultiple (e.g., two, three, four, and the like) cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., an eNodeB, UE, etc.) andsends a transmission of the data and/or other information to adownstream station (e.g., a UE or an eNodeB). A relay station may alsobe a UE that relays transmissions for other UEs. In the example shown inFIG. 1, a relay station 110 r may communicate with the eNodeB 110 a anda UE 120 r in order to facilitate communication between the eNodeB 110 aand the UE 120 r. A relay station may also be referred to as a relayeNodeB, a relay, etc.

The wireless network 100 may be a heterogeneous network that includeseNodeBs of different types, e.g., macro eNodeBs, pico eNodeBs, femtoeNodeBs, relays, etc. These different types of eNodeBs may havedifferent transmit power levels, different coverage areas, and differentimpact on interference in the wireless network 100. For example, macroeNodeBs may have a high transmit power level (e.g., 20 Watts) whereaspico eNodeBs, femto eNodeBs and relays may have a lower transmit powerlevel (e.g., 1 Watt).

The wireless network 100 may support synchronous operation. Forsynchronous operation, the eNodeBs may have similar frame timing, andtransmissions from different eNodeBs may be approximately aligned intime.

In one aspect, the wireless network 100 may support Frequency DivisionDuplex (FDD) or Time Division Duplex (TDD) modes of operation. Thetechniques described herein may be used for FDD or TDD mode ofoperation.

A network controller 130 may couple to a set of eNodeBs 110 and providecoordination and control for these eNodeBs 110. The network controller130 may communicate with the eNodeBs 110 via a backhaul. The eNodeBs 110may also communicate with one another, e.g., directly or indirectly viaa wireless backhaul or a wireline backhaul.

The UEs 120 (e.g., UE 120 x, UE 120 y, etc.) are dispersed throughoutthe wireless network 100, and each UE may be stationary or mobile. A UEmay also be referred to as a terminal, a user terminal, a mobilestation, a subscriber unit, a station, or the like. A UE may be acellular phone (e.g., a smart phone), a personal digital assistant(PDA), a wireless modem, a wireless communication device, a handhelddevice, a laptop computer, a cordless phone, a wireless local loop (WLL)station, a tablet, a netbook, a smart book, or the like. A UE may beable to communicate with macro eNodeBs, pico eNodeBs, femto eNodeBs,relays, and the like. In FIG. 1, a solid line with double arrowsindicates desired transmissions between a UE and a serving eNodeB, whichis an eNodeB designated to serve the UE on the downlink and/or uplink. Adashed line with double arrows indicates interfering transmissionsbetween a UE and an eNodeB.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition the system bandwidth into multiple(K) orthogonal subcarriers, which are also commonly referred to astones, bins, or the like. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (K) may bedependent on the system bandwidth.

FIG. 2 shows a downlink FDD frame structure used in LTE. Thetransmission timeline for the downlink may be partitioned into units ofradio frames. Each radio frame may have a predetermined duration (e.g.,10 milliseconds (ms)) and may be partitioned into 10 subframes withindices of 0 through 9. Each subframe may include two slots. Each radioframe may thus include 20 slots with indices of 0 through 19. Each slotmay include L symbol periods, e.g., 7 symbol periods for a normal cyclicprefix (as shown in FIG. 2) or 6 symbol periods for an extended cyclicprefix. The 2 L symbol periods in each subframe may be assigned indicesof 0 through 2 L−1. The available time frequency resources may bepartitioned into resource blocks. Each resource block may cover Nsubcarriers (e.g., 12 subcarriers) in one slot.

In LTE, an eNodeB may send a primary synchronization signal (PSC or PSS)and a secondary synchronization signal (SSC or SSS) for each cell in theeNodeB. For FDD mode of operation, the primary and secondarysynchronization signals may be sent in symbol periods 6 and 5,respectively, in each of subframes 0 and 5 of each radio frame with thenormal cyclic prefix, as shown in FIG. 2. The synchronization signalsmay be used by UEs for cell detection and acquisition. For FDD mode ofoperation, the eNodeB may send a Physical Broadcast Channel (PBCH) insymbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carrycertain system information.

The eNodeB may send a Physical Control Format Indicator Channel (PCFICH)in the first symbol period of each subframe, as seen in FIG. 2. ThePCFICH may convey the number of symbol periods (M) used for controlchannels, where M may be equal to 1, 2 or 3 and may change from subframeto subframe. M may also be equal to 4 for a small system bandwidth,e.g., with less than 10 resource blocks. In the example shown in FIG. 2,M=3. The eNodeB may send a Physical HARQ Indicator Channel (PHICH) and aPhysical Downlink Control Channel (PDCCH) in the first M symbol periodsof each subframe. The PDCCH and PHICH are also included in the firstthree symbol periods in the example shown in FIG. 2. The PHICH may carryinformation to support hybrid automatic retransmission (HARQ). The PDCCHmay carry information on uplink and downlink resource allocation for UEsand power control information for uplink channels. The eNodeB may send aPhysical Downlink Shared Channel (PDSCH) in the remaining symbol periodsof each subframe. The PDSCH may carry data for UEs scheduled for datatransmission on the downlink.

The eNodeB may send the PSC, SSC and PBCH in the center 1.08 MHz of thesystem bandwidth used by the eNodeB. The eNodeB may send the PCFICH andPHICH across the entire system bandwidth in each symbol period in whichthese channels are sent. The eNodeB may send the PDCCH to groups of UEsin certain portions of the system bandwidth. The eNodeB may send thePDSCH to groups of UEs in specific portions of the system bandwidth. TheeNodeB may send the PSC, SSC, PBCH, PCFICH and PHICH in a broadcastmanner to all UEs, may send the PDCCH in a unicast manner to specificUEs, and may also send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period.Each resource element may cover one subcarrier in one symbol period andmay be used to send one modulation symbol, which may be a real orcomplex value. For symbols that are used for control channels, theresource elements not used for a reference signal in each symbol periodmay be arranged into resource element groups (REGs). Each REG mayinclude four resource elements in one symbol period.

A UE may know the specific REGs used for the PHICH and the PCFICH. TheUE may search different combinations of REGs for the PDCCH. The numberof combinations to search is typically less than the number of allowedcombinations for all UEs in the PDCCH. An eNodeB may send the PDCCH tothe UE in any of the combinations that the UE will search.

A UE may be within the coverage of multiple eNodeBs. One of theseeNodeBs may be selected to serve the UE. The serving eNodeB may beselected based on various criteria such as received power, path loss,signal-to-noise ratio (SNR), etc.

FIG. 3 is a block diagram conceptually illustrating an exemplary FDD andTDD (non-special subframe only) subframe structure in uplink long termevolution (LTE) communications. The available resource blocks (RBs) forthe uplink may be partitioned into a data section and a control section.The control section may be formed at the two edges of the systembandwidth and may have a configurable size. The resource blocks in thecontrol section may be assigned to UEs for transmission of controlinformation. The data section may include all resource blocks notincluded in the control section. The design in FIG. 3 results in thedata section including contiguous subcarriers, which may allow a singleUE to be assigned all of the contiguous subcarriers in the data section.

A UE may be assigned resource blocks in the control section to transmitcontrol information to an eNodeB. The UE may also be assigned resourceblocks in the data section to transmit data to the eNode B. The UE maytransmit control information in a Physical Uplink Control Channel(PUCCH) on the assigned resource blocks in the control section. The UEmay transmit only data or both data and control information in aPhysical Uplink Shared Channel (PUSCH) on the assigned resource blocksin the data section. An uplink transmission may span both slots of asubframe and may hop across frequency as shown in FIG. 3. According toone aspect, in relaxed single carrier operation, parallel channels maybe transmitted on the UL resources. For example, a control and a datachannel, parallel control channels, and parallel data channels may betransmitted by a UE.

FIG. 4 shows a block diagram of a design of a base station/eNodeB 110and a UE 120, which may be one of the base stations/eNodeBs and one ofthe UEs in FIG. 1. For example, the base station 110 may be the macroeNodeB 110 c in FIG. 1, and the UE 120 may be the UE 120 y. The basestation 110 may also be a base station of some other type. The basestation 110 may be equipped with antennas 434 a through 434 t, and theUE 120 may be equipped with antennas 452 a through 452 r.

At the base station 110, a transmit processor 420 may receive data froma data source 412 and control information from a controller/processor440. The control information may be for the PBCH, PCFICH, PHICH, PDCCH,etc. The data may be for the PDSCH, etc. The processor 420 may process(e.g., encode and symbol map) the data and control information to obtaindata symbols and control symbols, respectively. The processor 420 mayalso generate reference symbols, e.g., for the PSS, SSS, andcell-specific reference signal. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 430 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols, if applicable, and may provide output symbol streamsto the modulators (MODs) 432 a through 432 t. Each modulator 432 mayprocess a respective output symbol stream (e.g., for OFDM, etc.) toobtain an output sample stream. Each modulator 432 may further process(e.g., convert to analog, amplify, filter, and upconvert) the outputsample stream to obtain a downlink signal. Downlink signals frommodulators 432 a through 432 t may be transmitted via the antennas 434 athrough 434 t, respectively.

At the UE 120, the antennas 452 a through 452 r may receive the downlinksignals from the base station 110 and may provide received signals tothe demodulators (DEMODs) 454 a through 454 r, respectively. Eachdemodulator 454 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 454 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 456 may obtainreceived symbols from all the demodulators 454 a through 454 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 458 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 460, and provide decoded control informationto a controller/processor 480.

On the uplink, at the UE 120, a transmit processor 464 may receive andprocess data (e.g., for the PUSCH) from a data source 462 and controlinformation (e.g., for the PUCCH) from the controller/processor 480. Theprocessor 464 may also generate reference symbols for a referencesignal. The symbols from the transmit processor 464 may be precoded by aTX MIMO processor 466 if applicable, further processed by the modulators454 a through 454 r (e.g., for SC-FDM, etc.), and transmitted to thebase station 110. At the base station 110, the uplink signals from theUE 120 may be received by the antennas 434, processed by thedemodulators 432, detected by a MIMO detector 436 if applicable, andfurther processed by a receive processor 438 to obtain decoded data andcontrol information sent by the UE 120. The processor 438 may providethe decoded data to a data sink 439 and the decoded control informationto the controller/processor 440. The base station 110 can send messagesto other base stations, for example, over an X2 interface 441.

The controllers/processors 440 and 480 may direct the operation at thebase station 110 and the UE 120, respectively. The processor 440 and/orother processors and modules at the base station 110 may perform ordirect the execution of various processes for the techniques describedherein. The processor 480 and/or other processors and modules at the UE120 may also perform or direct the execution of the functional blocksillustrated in use method flow chart shown in FIG. 5, and/or otherprocesses for the techniques described herein. The memories 442 and 482may store data and program codes for the base station 110 and the UE120, respectively. A scheduler 444 may schedule UEs for datatransmission on the downlink and/or uplink.

A number of methods may be employed to estimate a serving channel by aUE. One method is iterative soft cancellation of pilot signals. Suchiterative cancellation occurs as described below. A channel is estimatedusing the equation:y=h ₁ x ₁ +h ₂ x ₂ +n

where y is the received signal, x_(i) indicates known pilot signals,h_(i) indicates channel gain, and n indicates thermal noise. In a firstiteration, f₁, the estimate of h₁ is calculated from y. The estimatedinterference caused by h₁x₁ may then be cancelled from y. f₂, theestimate of h₂ is then calculated from y−f₁x₁. In a second iteration, anew f₁ (the estimate of h₁) is calculated from y−f₂x₂. A new f₂ (theestimate of h₂) is calculated from y−f₁x₁. These calculations maycontinue for N iterations where N is a chosen parameter and may beincreased or decreased depending on a desired accuracy/resource usetradeoff. A larger N yields an increased accuracy for channelestimation.

A soft cancellation factor α_(i) may be introduced where 0≦α_(i)≦1. Thesoft cancellation factor, α_(i), may be used in the above calculationssuch that instead of cancelling an entire signal h_(i)x_(i), a signalfraction α_(i)h_(i)x_(i) is cancelled. Selecting a cancellation factorless than 1 makes iterative cancellation more robust to large errors inchannel estimates. If the channel estimator is a biased estimator, asuitably chosen cancellation factor may help in bias removal.

A UE may be limited in the number of iterations it may perform duringchannel estimation. For example, the hardware in a UE may only becapable of performing a certain number of iterations within a particulartime period. According to an aspect of the disclosure, an improvedchannel estimation engine uses iterative soft cancellation for improvedchannel estimation of weak cells in the presence of strongerinterferers. The improved engine may be used with Long Term Evolution(LTE) systems. Iterative soft cancellation of pilot signals is used foraccurate and robust cancellation with priority given to certaincell/antenna pairs. As shown in block 502 of FIG. 5, certain cells maybe chosen to undergo iterative cancellation while others may beexcluded. Cells which are chosen are ordered to improve cancellationresults and resource utilization. Cells are classified and ordered basedon certain metrics, such as reference signal (RS) power. Complexityconstraints (such as a limited number of iterations within a certaintime period) may be applied to improve or optimize the number ofiterations for each cell and improve the obtained serving cellthroughput. Signals from cells determined to be more important mayundergo more iterations than signals from less important cells.

Cell classification and ordering may be accomplished in several ways. Asshown in block 504 of FIG. 5, a pair may be created for eachcell/antenna combination. For example, if a first cell has four antennasand a second cell has four antennas there are eight possiblecell/antenna pairs for those two cells (i.e., first cell, first antenna;first cell, second antenna; first cell, third antenna; first cell,fourth antenna; second cell first antenna; second cell, second antenna;second cell third antenna; and second cell, fourth antenna. An exampleof this pairing is shown in FIG. 6. Three cells, Cell 1 602, Cell 2 612,and Cell 3 622 are shown. Each cell has three antennas. Cell 1 602 hasAntenna A 604, Antenna B 606, and Antenna C 608. Cell 2 612 has AntennaA 614, Antenna B 616, and Antenna C 618. Cell 3 622 has Antenna A 624,Antenna B 626, and Antenna C 628. A UE within receiving distance of allthree cells, shown in FIG. 6 would identify nine different antennapairs:

(Cell 1, Antenna A) (Cell 1, Antenna B) (Cell 1, Antenna C) (Cell 2,Antenna A) (Cell 2, Antenna B) (Cell 2, Antenna C) (Cell 3, Antenna A)(Cell 3, Antenna B) (Cell 3, Antenna C)However, the ultimate determination of which of the nine differentantenna pairs a given UE identifies will depend on various factorsrelating to the three cells (e.g., geographic locations, signal power,cell IDs, etc.) as well as various factors relating to the UE (e.g., thelocation, configuration, and capabilities of the UE).

As shown in block 506 of FIG. 5, cell/antenna pairs may be ranked. Ametric may be computed to rank the pairs. One such metric is referencesignal (RS) power. Pairs may also be grouped into groups of pairs.

A threshold of transmission power may also be used to sort pairs. Forexample, as shown in block 508 of FIG. 5, an antenna of a cell that isbelow a certain configurable power threshold may be dropped from theinput list and discarded for purposes of channel estimation. Thistechnique may be used to prune lower power pairs and reduce thecomplexity of the eventual channel estimation method. The remainingpairs in the input list may be sorted in decreasing order according to asuitable metric, such as reference signal power.

As shown in block 510 of FIG. 5, the input list may then be partitionedinto groups, where each group consists of pairs whose pilot tones occupythe same time-frequency resource (i.e., collide). For example, in LTEthere are typically six resources on which pilots are sent. Antennaswhich use the same resource may be grouped. Groups that contain a pairof the serving cell are identified as serving-cell groups. Members of aserving-cell group may be estimated more accurately than other pairs,meaning given a fixed number of communication resources, more resourcesmay be allocated to the serving-cell group than to other groups. Groupsmay be ranked according to one or more metrics including whether a groupincludes a serving cell cell-antenna pair, the number of iterativeinterference cancellation capable cells included in the group, or a sumof the powers of reference signals of iterative interferencecancellation capable cells included in the group. Other metrics may alsobe used. Cell-antenna pairs within a group may also be ranked accordingto one or more metrics including whether a cell-antenna pair includes aserving cell, whether a cell-antenna pair includes an iterativeinterference cancellation capable cell, or the power of a referencesignal of a cell-antenna pair. Other metrics may also be used.

As shown in block 512 of FIG. 5, certain cell/antenna pairs may bemarked as non-iterative cancellation (non-IC) pairs. Interference causedby a non-IC pair is not cancelled out. Non-IC pairs are pairs that aretoo weak to estimate accurately even if stronger cells are cancelledout. Fake cells may also be marked as non-IC cells. Non-IC cells may begrouped, and criteria used to mark non-IC cells may be different acrossgroups. Criteria for marking pairs as non-IC pairs may include referencesignal power and whether the pair belongs to a serving group ornon-serving group.

As shown in block 514 of FIG. 5, each pair to undergo iterativecancellation (IC pairs) may be assigned a number of iterations forcancellation purposes. Each pair may be given a number of parameterssuch as (N_(max,s), N_(min,s), N_(max,ns), N_(min,ns)) where N_(max,s)is the maximum number of iterations for a serving group, N_(min,s) isthe minimum number of iterations for a serving group, N_(max,ns) is themaximum number of iterations for a non-serving group, and N_(min,ns) isthe minimum number of iterations for a non-serving group. Iterationnumbers may be initially assigned and adjusted later to meet desiredcomplexity constraints.

As shown in block 516 of FIG. 6, groups may then be staged to optimizethe number of iterations performed for grouped pairs. Groups may befirst ordered in descending order according to desired metrics. Onemetric for sorting groups may be whether the group contains the servingcell and/or the total reference signal power of IC pairs in the group.

For each group, two lists of stages are generated. A pair can appear inmultiple stages if it is allocated more than one iteration. A stage is asingle occurrence of a pair in an IC ordering. One stage list is for ICpair stages, which corresponds to the IC pairs, with each IC pairoccurring as many times as that pair is to be iterated. For example, ifthere are two pairs, Pair1 and Pair2, each to be given three iterations,the IC stage list would be six stages long: {Pair1, Pair2, Pair1, Pair2,Pair1, Pair2}. The second stage list is for non-IC pair stages, whichcorresponds to all non-IC pairs in sorted order, each appearing once.Continuing the above example, if there was a third pair, Pair3, whichwas a non-IC pair, the non-IC stage list would be one stage long:{Pair3}.

For cancellation purposes, the groups (typically numbering six in an LTEenvironment) may be mapped/assigned to a hardware block to performiterative channel estimation, as shown in block 702 of FIG. 7. Thismapping may be configurable, permitting load balancing to improveprocessing efficiency. If more than one hardware block is available,groups may be assigned to hardware blocks in sequence. Where K is thetotal number of groups (such as six in LTE), group k, where 1≦k≦K isassigned to the hardware block that is least loaded after assigninggroups 1 to k−1. Other measures of loading may be defined as desired.For example, loading may be determined by taking into account that ICcells with a higher metric, such as higher sums of reference signalpower, will create greater hardware loads. It may be desirable to assigngroups to hardware blocks in as even a manner as possible to balanceloads and avoid having too many important groups assigned to the samehardware block.

Certain hardware block constraints (such as a hardware block beinglimited to a certain number of stages within a certain time period) mayresult in deleting stages, as shown in block 704 of FIG. 7. Stages fromless important groups may be removed first.

Ordered stages are populated to hardware blocks to perform the softchannel estimation, as shown in block 706 of FIG. 7. The ordered stagelist is first populated with IC pairs of the groups in sorted order,followed by the non-IC pair list of the groups in sorted order. Bygrouping IC stages together in this manner, decoding of control/datachannels may begin earlier (i.e., once estimation of IC pairs iscompleted). Earlier decoding occurs because non-IC pairs do not impactdecoding because they are canceled out.

Following the assigning of ordered stages to hardware blocks, eachhardware block will be assigned N stages. If N is too large for aparticular hardware block, a pruning method may be used to meet desiredcomplexity constraints. The pruning method may use a metric to rankdifferent stages, and may successively prune lower ranked stages until adesired complexity constraint is met. The rank of a stage may be relatedto the rank of the group to which it belongs. Groups can be ranked inthe ordered stage generation procedure described above. One way toconstrain complexity of the method is to limit the number of stagesassigned to each hardware block to be less than a target number.

FIG. 8 is a flow diagram illustrating channel estimation according toone aspect. A UE determines cell-antenna pairs associated with receivedtransmissions in a received signal, as shown in block 802. The UE groupsthe cell-antenna pairs into groups, as shown in block 804. Each groupincludes cell-antenna pairs with colliding pilot tones. The UE ranks thegroups according to a determined metric, as shown in block 806. The UEassigns a number of iterations to each ranked group, as shown in block808. The UE performs channel estimation using iterative cancellation, asshown in block 810. In the iterative cancellation, receivedtransmissions from cell-antenna pairs in a higher ranked group areiterated first, and received transmissions from cell-antenna pairs areiterated over their assigned number of times.

In one configuration, the UE 120 is configured for wirelesscommunication including means for determining cell-antenna pairsassociated with received transmissions in a received signal, means forgrouping the pairs, means for ranking the groups, means for assigningiterations to each group, and means for performing channel estimationusing iterative cancellation. In one aspect, the aforementioned meansmay be the processor(s), the controller/processor 480, the memory 482,the receive processor 458, the demodulators 454 a and 454 r, and theantennas 452 a and 452 r, configured to perform the functions recited bythe aforementioned means. In another aspect, the aforementioned meansmay be a module or any apparatus configured to perform the functionsrecited by the aforementioned means.

FIG. 9 shows a design of an apparatus 900 for a UE, such as the UE 120of FIG. 4. The apparatus 900 includes a module 902 to determinecell-antenna pairs associated with received transmissions in a receivedsignal. The apparatus also includes a module 904 to group thecell-antenna pairs into groups. Each group includes cell-antenna pairswith colliding pilot tones. The apparatus also includes a module 906 torank the groups according to a determined metric. The apparatus alsoincludes a module 908 to assign a number of iterations to each rankedgroup. The apparatus also includes a module 910 to perform channelestimation using iterative cancellation. In the iterative cancellation,received transmissions from cell-antenna pairs in a higher ranked groupare iterated first, and received transmissions from cell-antenna pairsare iterated over their assigned number of times. The modules in FIG. 9may be processors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, software codes, firmware codes,etc., or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of wireless communication in a wirelessnetwork, the method comprising: determining cell-antenna pairsassociated with received transmissions in a received signal; groupingthe cell-antenna pairs into groups, each group including cell-antennapairs with pilot tones that occupy the same time-frequency resource;ranking the groups according to a determined metric; assigning a numberof iterations to each ranked group; and performing, by a processor,channel estimation using iterative cancellation, in which receivedtransmissions from cell-antenna pairs in a higher ranked group areiterated first, and received transmissions from cell-antenna pairs areiterated over an assigned number of times for each respectivecell-antenna pair.
 2. The method of claim 1 in which the determinedmetric is at least one of: whether a group includes a serving cellcell-antenna pair; a number of interference cancellation capable cellsincluded in the group; and a sum of powers of reference signals ofinterference cancellation capable cells included in the group.
 3. Themethod of claim 1 in which cell-antenna pairs within a group are orderedaccording to at least one of: whether a cell-antenna pair includes aserving cell; whether a cell-antenna pair includes an interferencecancellation capable cell; and a power of a reference signal of acell-antenna pair.
 4. The method of claim 3 in which orderingcell-antenna pairs within a group comprises indicating a selected lowerranked cell-antenna pair as a non-iterative cancellation cell-antennapair.
 5. The method of claim 1, in which the iterative cancellation isperformed by partially cancelling received transmissions during eachiteration.
 6. The method of claim 1 further comprising assigning zeroiterations to received transmissions that fall below a defined signalstrength parameter.
 7. The method of claim 1 further comprisingassigning iterations to hardware resources and adjusting assignediterations to achieve a desired complexity constraint.
 8. The method ofclaim 1 further comprising creating a processing stage which comprisesone entry for each number of assigned times a received transmission isto be iterated.
 9. An apparatus for wireless communication, comprising:means for determining cell-antenna pairs associated with receivedtransmissions in a received signal; means for grouping the cell-antennapairs into groups, each group including cell-antenna pairs with pilottones that occupy the same time-frequency resource; means for rankingthe groups according to a determined metric; means for assigning anumber of iterations to each ranked group; and means for performingchannel estimation using iterative cancellation, in which receivedtransmissions from cell-antenna pairs in a higher ranked group areiterated first, and received transmissions from cell-antenna pairs areiterated over an assigned number of times for each respectivecell-antenna pair.
 10. The apparatus of claim 9 further comprising meansfor assigning iterations to hardware resources and means for adjustingassigned iterations to achieve a desired complexity constraint.
 11. Acomputer program product for wireless communication in a wirelessnetwork, comprising: a non-transitory computer-readable medium havingnon-transitory program code recorded thereon, the program codecomprising: program code to determine cell-antenna pairs associated withreceived transmissions in a received signal; program code to group thecell-antenna pairs into groups, each group including cell-antenna pairswith pilot tones that occupy the same time-frequency resource; programcode to rank the groups according to a determined metric; program codeto assign a number of iterations to each ranked group; and program codeto perform channel estimation using iterative cancellation, in whichreceived transmissions from cell-antenna pairs in a higher ranked groupare iterated first, and received transmissions from cell-antenna pairsare iterated over an assigned number of times for each respectivecell-antenna pair.
 12. The computer program product of claim 11 furthercomprising program code to assign iterations to hardware resources andprogram code to adjust assigned iterations to achieve a desiredcomplexity constraint.
 13. An apparatus for wireless communication,comprising: a memory comprising non-transitory computer executableinstructions; and at least one processor coupled to the memory, the atleast one processor being configured, upon execution of theinstructions: to determine cell-antenna pairs associated with receivedtransmissions in a received signal; to group the cell-antenna pairs intogroups, each group including cell-antenna pairs with pilot tones thatoccupy the same time-frequency resource; to rank the groups according toa determined metric; to assign a number of iterations to each rankedgroup; and to perform channel estimation using iterative cancellation,in which received transmissions from cell-antenna pairs in a higherranked group are iterated first, and received transmissions fromcell-antenna pairs are iterated over an assigned number of times foreach respective cell-antenna pair.
 14. The apparatus of claim 13 inwhich the determined metric is at least one of: whether a group includesa serving cell cell-antenna pair; a number of interference cancellationcapable cells included in the group; and a sum of powers of referencesignals of interference cancellation capable cells included in thegroup.
 15. The apparatus of claim 13 in which cell-antenna pairs withina group are ordered according to at least one of: whether a cell-antennapair includes a serving cell; whether a cell-antenna pair includes aninterference cancellation capable cell; and a power of a referencesignal of a cell-antenna pair.
 16. The apparatus of claim 15 in whichthe at least one processor is further configured to indicate a selectedlower ranked cell-antenna pair as a non-iterative cancellationcell-antenna pair.
 17. The apparatus of claim 13, in which the iterativecancellation is performed by partially cancelling received transmissionsduring each iteration.
 18. The apparatus of claim 13 in which the atleast one processor is further configured to assign zero iterations toreceived transmissions that fall below a defined signal strengthparameter.
 19. The apparatus of claim 13 in which the at least oneprocessor is further configured to assign iterations to hardwareresources and adjusting assigned iterations to achieve a desiredcomplexity constraint.
 20. The apparatus of claim 13 in which the atleast one processor is further configured to create a processing stagewhich comprises one entry for each number of assigned times a receivedtransmission is to be iterated.